Interlocking system for railroads



15, 1938 s. N. WIGHT INTERLOCKING SYSTEM FOR RAILROADS Filed May 28, 1937 2 Sheets-Sheet l INVENTOR 46 BY 2:: ATTORNEY f in Patented Mar. 15, 1938 V 2,111,501. INTERLOCKING SYSTEM FOR RAILROADS SedgwickN. Wight, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application May 28, 1937, SerialNo. 145,337 I 13 Claims. (01. 246-134) This inventionrelates to interlocking systems for railroads, and more particularly pertains to an interlocking system which can bel'o'perated by either automatic traffic conditions or manual manipulation of control means.

A'provision is made by this invention whereby an interlocking system can be operated automatically by trains entering approach sections; or'upon reversing a switch inithe control oifice, the interlocking system canbe manually controlled from a central office by control buttons for the entrance and exit ends of the several routes of the track layout. The present invention employs features disclosed. in my prior application Ser. No. 721,696 filed April 21, 1934, but no claims are made herein to any invention disclosed in my said prior application.

A system of this character is particularly useful at those interlocking plants where trafiic is generally light, but at certain times becomes so dense as to require the control of the plant by an operator.

One of the objects of the present invention is to provide a system of this type so organized as to be particularly adaptable to the entrance-exit type of manipulation as well as adaptable to automatic control by train presence, and to have as much of the apparatus'as possible'common to both sets of contro-l'means.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

The accompanying drawings showone embodiment of the present invention as applied to' a railway track layout in which each track is signalled for trafiic in both directions.

Fig. 1 shows the apparatus located in the control office.

Fig. 2 shows the apparatus located at the field track layout.

With reference to Fig. 2, a diverging track I! is illustrated as having a track circuit 4 and connected to a main track I8 by means of the track switch TS. Track [8 is divided intotrack circuits 2, l and 3, and is crossed by track l9 which is divided into track circuits 5 and B as well as having a section incommon with track circuit 1.

Each of these track circuits is provided With the usual track relay T and a track battery. The track relays T are indicated as associated with their respective track sections by their distinguishing preceding numerals.

The track layout is provided with signals, of

the color light type for governing traffic through the interlocking plant in both directions on each track. Signal IOA governs east-bound traific over track It, while signal I l governs west-bound trafiic. Signals [OB and I2 govern traffic over tracks I! and I8 by way of the track switch TS, signal IBB governing east-bound traific and signal I2 governing west-bound trafiic. Signals l3 and M govern trafiic over track I9, signal l3 governing south-bound traific and signal l4 governing north-bound trafiic.

Each signal has a stick relay S associated therewith to prevent that signal from automatically clearing when a train is leaving the interlocking plant. A push button PB is provided for each stick relay to release its associated signal for clearing in the event a leaving train desires to reverse its direction and reenter the plant. V .The switch machine SM provides for the power operation of the track switch TS, and is controlled by a two position polar relay Z in a similar manner as the switch machine SM in the Patent No. 1,975,137 dated October 2, 1934, is controlled by its lever SML. The switch machine SM may be of any suitable type, such as shown in the patentto W. K. Howe, Patent No. 1,466,903, dated September 4, 1923.

A polar neutral relay WP is associated with the switch machine SM and the track switch TS for repeating the position of the track switch points in correspondence with the operating mechanism of the switch machine SM, the relay being energized with one polarity when the track switch is in its normal position and locked, and energized'with the other polarity when the track switch isin its reverse position and locked. The relayfWP is deenergized during the operation of the track switch and also at such other times as the track switch points are unlocked.

The present invention contemplates that suitable approach and detector locking is employed to protect against the operation of the track switch TS while it is unsafe for such operation. Thus, a lock relay L has been shown as interrupting the control for the switch machine SM when it is deenergized, and it is deenergized whenever a signal is cleared to allow the passage of traffic over the track switch TS and whenever the track section I is occupied by a train. When approach looking with time release is employed, the relay L is not reenergized until after a predetermined time has elapsed following the putting to stop of the governing signal.

A push-button Ill-[2P3 is located near signal ID and is operated by a trainman, while the system is set for automatic control and a train is standing on approach section 2, to set up a route over track switch 'TS in a reverse position between signals Ill and I2.

Referring to Fig. 1, the control machine is provided with a control panel upon which a track diagram is located corresponding to the actual track layout in the field. Entrance buttons N and exit buttons X are located on the control panel for the ends of the routes, while indicators TK advise the operator of the conditions of occupancy for their respective track sections as shown in my prior application Ser. No. 69,905 filed March 20, 1936. A signal indicator SK is located in the center of each of the entrance buttons N, and is illuminated when its corresponding signal is cleared. The control of these indicators TK and SK has not been shown, but may be as shown in my above mentioned prior application.

Route relays Iii-I I, I-I2 and I3l4 are of the polarized neutral type and are used in selecting and interlocking the several routes under both manual and automatic conditions of operation.

Relays AR and ASR are used in setting up a route for a train when the interlocking is under automatic operation.

A switch SW is used in transferring the interlocking system from manual to automatic operation when actuated to its opposite positions M and A respectively.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and the arrangement of parts that would be employed in practice. Thus, the various relays and buttons with their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries, or other sources of electric current, instead of showing all of the wiring connections to these terminals.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used always have currentfiowing in the same direction.

It is believed the nature of the invention, its advantages and characteristic features can be best understood with further description being set forth from the standpoint of operation.

Operation Under normal conditions with the track sections unoccupied all of the track relays. are energized and the track switch TS is in either a normal or a reverse position depending upon the last route set up. The track occupancy indicator lamps TK, and signal indicator lamps SK on the control panel are normally deenergized, thereby giving a so-called dark board.

Assuming an operator wishes to control the interlocking plant by means of the entrance and exit buttons located on the control panel, he must first operate the transfer switch SW to position M, doing so only at times when the indicator lamps on the control panel indicate that no signals have been cleared by reason of the presence of trains on the approach sections.

Having thus positioned the transfer switch SW, let us assume that a train is approaching signal II] on track I8 to a position where the track relay 2T is dropped away causing indicator ZTK to be illuminated. This advises the operator of the presence of a train. The operator now proceeds to set up a route for the train on track I8 by first turning the entrance button ION in a clockwise direction and then pressing the exit button for the end of the route where he wishes the train to leave the interlocking plant. Assuming he wants the train to leave on track I8, he presses the exit button I IX.

A circuit is now closed for energizing route relay IO-II from through a circuit including contact 20 of switch SW, contact 2| of entrance button IBN, winding of route relay Ill-II, back contact 22 of route relay I3-I4, back contact 23 of route relay II)-I2, back contact 41 of entrance button IIN, back contact 24 of exit button IIX, contact 25 of switch SW, to When relay I0II picks up, a stick circuit is closed from through a circuit including contact 2|! of switch SW, front contact 2| of entrance button IUN, winding of route relay IIl-II, back contact 22 of route relay I3-I4, back contact 23 of route relay I0 I2, right contact 26 of route relay IIJII, front contact 21. of relay I0I I, contact 25 of switch SW, to

The route relay I0--II being picked up closes a circuit for energizing the switch control relay Z from through a circuit including front contact 28 of relay I0I I, lower winding of relay Z, to The relay Z is a polar relay with two separate windings differentially connected so that energization of its lower Winding causes its contacts .to assume a polar position which will cause the switch machine SM to operate to its normal position, while energization of its upper winding causes its contacts to be operated to opposite positions to cause the reverse operation of the switch machine SM. The relay Z controls the switch machine SM by a circuit heretofore referred to as being shown more in detail in the prior Patent. No. 1,975,137, and mentioned as including a selection through the front contact of a lock relay L, the control of which look relay should necessarily include such de tector and approach locking as the particular condition may require.

Each signal has been shown as having gree and red lamps controlled respectively by the front and back contacts of a signal control relay G (not shown). "The control for each signal control relay G (not shown) has been indicated by dotted lines as including front and polar selections of the proper route relay, and a front contact of the detector track relay.

Assuming that the track switch TS has properly responded to the relay Z so that relay WP indicates the switch to be in a normal locked position, then a circuit is closed for the control of signal IDA from through a circuit including front contact 29 of relay WP, polar contact 30 of relay WP in a right hand position, front contact 3I of route relay Ill-II, polar contact 32 of relay I Il-II in a right hand position, a front contact 1-1 on track relay IT, to the signal control relay (not shown), the energization of which clears signal IDA.

The fact that signal IIJA has been cleared is indicated to the operator in the control office 2,1=11;5.o1 by the illumination of the lamp IUSK located within the button ION onthe control panel, thus indicating that the route has been completely set up. i

- When the train accepts the signal IDA, the track indicator lamp 'ITK on the control panel is illuminated to inform the operator that the train has accepted the signal, at which time the operator may return his entrance button HJN to its normal position,

However, the dropping of the detector track TI had already opened the control circuit of signal lllA at open front contact El causing the green lamp to be extinguished and the red lamp illuminated.

Theoperator may at this time, if he so desires, operate the entrance-exit control buttons for setting up another route. The signal controlling the new. route, however, will not clear until the detector track section has been unoccupied, and until the switch TS has been operated to its proper position and locked, if the new route includes that track switch.

Assuming the train to have left the interlocking plant and another train to have entered approach section 2 on the same track, the operator may set up a route for the approaching train over the track switch TS in its reverse position to track I! by first turning button HlN in a clockwise direction and pressing exit button IZX. v

The pressing of button 12X closes a circuit for energizing route relay .Hll2 from through a circuit including contact 2B of switch SW in position M, front contact 2! of button iElN, back contact 33 of relay I ll-l I, back contact 3d of relay i3--l4, winding of relay Ill-l2, back contact 48 of button IZN, back contact of button l2X, contact 25 of switchSW in position M, to lll!2 closes its stick circuit from through a circuit including contact 20 of switch SWin position M, front contact 2! of button lllN, back contact 33 of relay I U'-ll, back contact 34 of relay l3l4, winding of relay Ill-42, polar contact 36 of relayl0l2 in a right hand position, front contact 31. of relay llll2,'contact 25 of switch SW in position M, to,(-). 1

The relay Ill--l2 now effects the operation of the track switch TS at its reverse position by energizing the relay. Z to its left hand polar position by a circuit closed from through'a circuit including front contact 16 of relay HJI2, upper winding of relay Z, to The polar contacts of relay Z in their left hand positions close a circuit "(not shown) for reversing the track switchTS With the track switch TS in its reverse position and looked. a circuit is closed for clearing signal IUB from through a circuit including front contact 2 9 of relay WP, polar contact 30 of relayWPin a left handdotted position,

front contact 38 of relay ll3l2, polar contact 39 of relay IEII2 in a'right hand position, front contact '19 of relay IT, to. the control relay of.

signal IUB, which in turn clears signal 19B.

The clearing of signal 1 M3 illuminates the indi-,

cator light IGSK located in the entrance button lllN informing the operator that the route hasbeen'completely setup and the signal cleared.

In 'a similar manner, the operator may setup 'a route between signals l3 and M by operating entrance button I3N in a clockwise direction and pressing exit-button l lX thus closing a circuitforenergizing route relay IS-T-M, fr,om

The picking up of route relay through a circuit including contact 20 of switch SW in position M, front contact 40 of button ISN, back'contact 4| of relay lll-ll, winding of relay l3l l, back contact 42 of relay Ill-42, back contact 50 of button MN, back contact 43 of button MX, contact 25 of switch SW in position M, to The picking up of relay !3-l4 closes a stick circuit from through a circuitincluding contact 20 of switch SW in position M, front contact Ml of button ISN, back contact 41 of. relay Ill-4|, winding of relay l3l4, back contact 42 of relay l0-I2, polar contact 43 of relay I3I4 in a right hand position, front contact 44 of relay [3-44, contact 25 of the switch SW in position-M, to

The relay l3-I4 being picked up energizes the circuit for the control of signal l3 from through a circuit including front contact 45 of relay l3.l4,- polar contact 46 of relay l3-l4 in. a right hand position, to the control relay (not shown) of signal l3 which in turn clears signal l3. 7

From the above description, it will be noted that the route relays are electrically interlocked so that only one route relay may be energized at any time, the control of each relay being selected through back contacts of all the route relays for opposing or conflicting; routes. These interlocking contacts are included in both the pick up and stick circuits of the route relays. Havingthus described in detail the operation of the system under manual control for routes set up from east to west and north to south, it is to be understood that a similar operation occurs in setting up routes for trafiic from west to east the route relays in opposite positions.

. Assuming the trafiic conditions to be such that the control of the interlocking system by an operator is no longer required, the operator transfers the system to automatic operation by actuating the transfer switch SW to position A, first checking the control panel to see that the track occupancy lamps are'dark and that no routes have been set up by means of the entrance and exit buttons.

Under both automatic and manual operation the same route relays are used and the same switch and signal control circuits are employed. The transfer switch determines Whether the energy for the route relays is tobe applied through the control buttons under manual operation or through the contacts of the approach relays under automatic operation. In other words, the approach relays AR and ASR are used to take the place of the control buttons when the interlocking system is under automatic control. The route relays are interlocked in such a way as to permit the relays for no two conflicting routes to be energized at the same time, the same as under manual operation. If a condition should exist thatthe approach sections on two conflicting routes should become occupied at the same time, although the route relays for both routes try to pick up, the difference in the characteristics of the relays would allow one to gain preference over the other in a very short interval of time.

Assuming a train to approach signal Ill on track I8, the dropping of track relay 2T energizes the approach relay ROAR, from through a circuit including back'oontact 5! of relay Ills, back'icontact: 52 of relay 2T, back contact. 53 of I been set up, andto set up the desireddiverging relay I2AR, back contact 54 of-frelay I IAR, contact 55 of push button I0'-I2PB in itsnormal position, back contact 55 of relay. ISASR, winding of relay I OAR, contact 51 of switch SW in position A, to-().

Having picked up the approach relay IUAR, a circuit is closed for energizing route relay I0I I from througha circuit including contact 20 of switch SW in position A, front. contact 58 of relay I OAR, winding of relay. Iil'-.-I I, back contact 22 of relay I3-I4, backcontact 23 of relay I tI2, front contact 59 of relay IGAR, contact 25 of switch SW in position A, to

Having thus picked up route relay IIl-II, the

positioning of the switch and clearing of signal I DA will take place in a manner the same as previously described when the interlocking system was under manual control.

When using the approach sections at the opposite ends of a route as a means of automatically setting up that route and determining the direction of trafiic in it, a means must also be provided whereby a train leaving the route and dropping the approach track relay on the leaving end of the route will not set up that route for a train movement in the opposite direction. Such a condition, of course, would prevent the setting up of other routes by trains approaching such other routes.

A relay S is associated With each signal and energized whenever a route relay sets up traffic opposing such signal, and is maintained energized by a stick circuit closed until the train has left the interlocking plant. This relay S for a signal prevents the approach section for such signal from being effective when a train is moving against such signal.

For example, with route relay II)I I picked up a circuit is closed for energizing relay IIS from through a circuit including front contact 60 of relay IGI I, polar contact SI of relay IDI I in a right hand position, winding of relay II S, to

The train accepting signal IIlA drops track relay IT which in turn closes a stick circuit for relayIIS from through a circuit including front contact 62 of push button IIPB', back contact 63 of relay IT, front contact 64 of relay IIS, winding of relay IIS, to

The dropping of the track relay IT also opens the control of signal IBA thus causing the green lamp to be extinguished and'the red lamp. to be illuminated.

When the train leaves track section 2, relay II)-II is deenergized due to the opening of the circuit at front contacts 58 and 590i approach relay IIJAR, which in turn has been deenergized by the opening of back contact 52 of relay 2T.

As the train proceeds through the route and drops track relay 3T the circuit is held open for the control of relay I IAR at back contact 65'of relay I I S, which relay I IS is maintained picked up with relay 3T down by a circuit closed from through a circuit including front-contact 62 of push button I IPB, back contact 66 of relay 3T, front contact 84 of relay IIS, winding of relay IIS, to

When the train leaves track section 3, the system of course restores to normal conditions.

Assuming a train on track section 2 desires to go over the route to track H, a trainman operates the push button IIlI2PB, which is located near signal ID, to thereby release the through route on track I8 which has already route. This is done bydropping the approach relay IIIAR and picking up the approach relay IO'ASR, thus in turn dropping route relay Ill-II and picking up route relay IUI2. Relay IOAR is deenergized through the opening of front contact 55 of push button I0-I2PB, while the circuit for the control of relay III-II is opened at front contacts 58 and 59 of relay IDAR.

The relay. IOASR is energized when the push button I Il-I2PB is pressed through a circuit closed from including back contact 5I of relay IIIS, back contact 52 of relay 2T, back contact 53 of relay IZAR', back contact 54 of relay IIAR, back contact 55' of push button I0I2PB, back contact 6! of relay IUAR, winding of relay IOASR, contact 51 of switch SW, to As soon as relay IBASR picks up a stick circuit is closed for. shunting out push button I0I2PB from through a circuit including back contact 5I of relay IDS, back contact 52 of relay 2T, back contact 53'of relay IZAR, back contact 54 of relay I IAR, front contact 68 of relay I OASR, winding of relay IUASR, contact 57 of switch SW, to

Relay I OASR being picked up applies energy to route relay Ill-I2 by a circuit closed from through a circuit including contact 20 of switch SW in position A, front contact 69 of relay IDASR, back contact 33 of relay I IlI I, back contact 34 of relay I3-I4, windings of relay IIJI2, front contact III of relay IOASR, contact 25 of switch SW in position A, to Relay IIlI2 in a picked up position governs the control of signal IIlB and track switch TS through the same circuits, as previously described.

When signal IIlB clears after the operation of the track switch TS to a reverse position, the train proceeds over the route in the usual way. It is of course understood that relay I2S acts in the same manner as already described for relay IIS.

As approach relay IUASR is held in its energized position through its stick circuit which is dependent upon contact 52 of relay 2T the same as approachrelay I GAR, the relay IOASR will drop as soon astrack relay 2T picks up, thus releasing the approach relays for conflicting routes which were electrically interlocked by relay IUASR being inits energized position.

It is evident that the dropping of relay IUASR will allow the next trainapproaching on section 2 to automatically setup a through route on track IS, in the usual way. In other words, the actuation of the pushbutton IO'I2PB while a train is on section 2, is effective to set up the diverging route only for that train.

A train approaching signal I3 on track I 9 and dropping track relay 5T energizes route relay I3I4, if all conflicting route relays are down.

More specifically, the dropping of relay 5T closes a circuit for energizing relay I3AR from through a circuit including back contact II of relay I3S, back contact I2 of relay 5T, back contact I3 of relay MAR, winding of relay I3AR, contact 5! of switchSW in position A, to

Relay I3-I4 is now energized from through a circuit including contact 20 of switch SW in position A, front'contact I4 of relay I3AR, back contact 4| of relay Ill-I I, winding of relay I3-I I, back contact 42 of relay I0I2, front contact I5 of relay I3AR, contact 25 of switch SW in position A, to

Relay I3--I4.effects the clearing of signal I3 as heretofore described when the interlocking plant was under manual control, so that the train can proceed over the route as usual.

Having thus described in detail circuits for train movement from east to west and north to south, it is evident that operation for the reverse directions is similar, using the same circuits with the opposite polarity applied to the route relays, and using the approach relays AR and stick relays S to accomplish that automatic control.

Each signal has associated therewith a pushbutton PB for dropping the associated stick relay S in cases where a train desires to reenter the interlocking plant while the system is under automatic operation. Each push button is located near its signal so as to be readily accessible to a trainman.

For example, an east bound train having passed through the interlocking plant from the track section 1 into the track section 3, may set up a west bound route by pressing,the push button IIPB. This causes the stick circuit of relay HS to be opened at front contact-62 of push button HPB, which in turn drops relay HS to close the circuit for energizing approach relay HAR at back contact 65 of relay HS, thus allowing a route to bet set up in the samemanner, as under normal operation, by the closed condition of back contact 18 of relay 3T.

Having described one form of a traffic controlling system for railroads as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a trafiic controlling system for railroads, a track layout having a plurality of conflicting routes, signals for governing trafiic over said routes, an approach section for each of said routes, a route relay for each of said routes, automatic means for energizing each particular route relay when a train occupies said approach section for that route providing said automatic means is rendered effective, manually operable means for energizing each particular route relay providing said manually operable means is rendered effective, a contactor for at times rendering effective said automatic means and at other times rendering effective said manually operable means, circuit means for interlocking said route relays so as to allow only one of said route relays to be energized at any one time, and circuit means for clearing the signal for each particular route when said route relay for that route is energized.

2. In a traflic controlling system for railroads; a track layout having a plurality of conflicting routes; signals for governing traflic over said routes; an approach section for each of said routes; a route relay for each of said routes; automatic means for energizing each route relay when a train occupies its respective approach section providing said automatic means is rendered effective; a manually controlled button for the entrance end of each route; a manually controlled button for the exit end of each route; control means responsive, when rendered effective, to the joint operation of said entrance button and said exit button for any'parti uiar te for energizing said route relay for that particular route; a manually operable contactor for at times rendering said route relays responsive to said automatic means and at other times rendering said route relays responsive to said control means; circuit means for allowing only one of said route relays to be energized at any one time; and circuit means responsive to the operation of each of said route relays for energizing the signal for that route.

3. In a trafiic controlling system for railroads; a track layout having two stretches of track connected by a track switch to thereby form two routes, a power operated switch machine for operating said track switch, signals for governing trafiic over said routes, an approach track section for each route, a route relay for each route, automatic means for energizing each route relay when a train occupies the approach section for that particular route providing said automatic means is rendered efiective, manually operable means for energizing each route relay providing said manually operable means is rendered effective, contact means for at times rendering said route relays responsive to said automatic means and at other times rendering said route. relays responsive to said manually operable means, circuit means for allowing the energization of only one route relay at any one time, circuit means responsive to the operation of said route relays for controlling said switch machine to set up the route 'corresponding to the particular route relay then energized, and circuit means responsive to the operation of said route relays and said'track switch for controlling said signals.

4. In a trafiic controlling system for railroads, a track layout having a first stretch of track crossed by a second stretch of track, signals for governing traific in both directions over each track, an approach section for each signal, a route relay for each track, automatic means for at times distinctively energizing said route relay in accordance with whether a train occupies one or the other of said approach sections for that track, a manually operable means for at other times distinctively energizing each route relay,

manually operable contact means for determining which times said automatic means and said manually operable means are to be respectively rendered effective, circuit means for allowing only one route relay to be distinctively energized at any one time, a detector track section having a track relay, and circuit means for selecting and controlling the signal for each track responsive only to the distinctive energization of the route relay for that track and the condition of said track relay.

5. In an interlocking system for railroads; a track layout having a plurality of conflicting routes; certain ones of which include at least one track switch; signals for governing traffic over said routes; an approach track section for each of said routes; a route relay for each of said routes; circuit means associated with each approach track section and rendered effective by a train in such section to energize its route relay, said means allowing only one of said route relays to be energized at a time; means for controlling said track switch to a proper position for each route over it when the route relay for that route is energized; and means for clearing the signal for each route when its route relay is energized, said means acting to clear the signal for a route over said track switch only when said track switch is in a proper position for that route. 7

6. In an interlocking system for railroads; a first stretch of track crossed by a second stretch of track, signals governing traffic in both directions over each stretch of track, approach track sections in approach to each said signals, a route relay for each track, automatic means responsive to a train for energizing that one of said route relays corresponding to the approach track section for that track which is occupied by a train, means allowing only one of said route relays to be energized at a time, a lookout means for preventing the approach track section for a particular track from being efiective to energize a route relay when that route is occupied by a train leaving the route, a manually operated means for at times rendering said lockout means ineffective, and a means for controlling said signals responsive to the operation of said route relays.

'7. In an interlocking system for railroads; a track layout having a plurality of conflicting routes; signals for governing traffic over said routes; an approach track section for each of said routes, certain of said approach sections being common to two routes; a route relay for each of said routes; circuit means responsive to the presence of a train for energizing each route relay when its said approach track section is occupied, said means allowing only one of said route relays to be energized at a time; manually operated means for energizing a second of two route relays when the first relay has been automatically energized providing that the occupied approac'h section is common to both routes, said means effecting the deenergization of said first route relay; and means for clearing the signal for each route when its route relay is energized.

8. In an interlocking system for railroads, a first stretch of track crossed by a second stretch of track, signals governing trafiic in both directions over each stretch of track, approach track sections in approach to each of said signals, a route relay for each track, automatic means for energizing a given route relay when either of the approach track sections for that track is occupied by a train, means allowing only one of said route relays to be energized at a time, lockout means for preventing the approach track section for a particular track from being efiective to energize its route relay when that route is occupied by a train leaving the route, and means for clearing the signal for one direction or the other for a particular stretch of track when its route relay is energized depending upon whether such route relay is energized in response to the occupied condition of one approach track section or the other, whereby a train automatically causes the clearing of a signal upon approach to that signal and can pass through the route established thereby Without clearing the signal for the opposite direction. I

9. In an interlocking system for railroads, a first stretch of track crossed by a second stretch of track, signals governing trafilc in both directions over each stretch of track, approach track sections in approach to each of said signals, a route relay for each track, automatic means for energizing each route relay when either of the approach track sections for that track is occupied by a train, means allowing only one of said route relays to be energized at a time, lockout means for preventing the approach track section for a particular track from being effective to energize its route relay when that route is occupied by a train leaving the route, means for clearing the signal for one direction. 01 the other for a particular stretch of' track when its route relay is energized depending upon whether such routerelay is energized in response to the occupied condition of one approach track section or the other, whereby a train automatically causes the clearing of a signal upon approach to that signal and can pass through the route establlished thereby without clearing the signal for the opposite direction, manually operable means associated with each of said approach track sections for at times rendering its lockout means ineffective, whereby a train after having passed through a route, may re-enter that route in the opposite direction.

10. In an interlocking system for railroads; a track layout having two conflicting routes interconnected by a track switch; signals for governing trafiic over said routes; an approach track section common to both said routes; a route relay for each of said routes; circuit means controlled by' a train on said common approach track section for energizing a particular one of said route relays when said approach track section is occupied; manually operable means for at times deenergizing said one route relay and energizing the other; means for controlling said track switch to a proper position for each route over it when the route relay for that route is energized; and means for clearing said signals for said routes when their corresponding route relays are energized.

11. In a traffic controlling system for railroads; a plurality'of tracks forming a plurality of 'confiicting routes, signals governing traffic in both directions over each route, a route relay for each route, automatic means responsive to the presence of a train for energizing each route relay with one polarity or the other in accordance with whether a train approaches one signal or the other governing traffic over the corresponding route, said automatic means being eii'ective only when all conflicting route relays are deenergized, and means responsive to the polarity of energization of each route relay for selecting the signal to be cleared for its route.

12. In a trafiic controlling system for railroads; a track layout having a plurality of conflicting routes; signals for governing traffic over said routes; an approach section for each signal; route establishing means for each of said routes for setting up its respective route and clearing a signal governing trafiic thereover when actuated; automatic means for actuating said route establishing means when a train occupies the approach section to that route providing said automatic means is rendered eflective: control buttons for the opposite ends of each of said routes; means responsive to the joint operation of the control buttons for the opposite ends of each route for actuating said route establishing means for that route providing said control buttons are rendered effective; means for at times rendering said automatic means efiective and at other times rendering said control buttons effective; and circuit means for allowing only one of said route establishing means for said conflicting routes to be actuated at the same time.

13. In a traffic controlling system for railroads, a track layout having a plurality of conflicting routes, signals located at the opposite ends of each route for governing traffic over said routes in both directions, an approach track section for each of said signals, a route relay for each of said routes, a manually operable contactor capable of assuming either of two positions, automatic means responsive to the presence of a train on one or the other of the approach track sections at the opposite ends of a route for energizing the route relay for the intervening route with one polarity or the other, said means being rendered effective only when said manually operable contactor is in one of its two positions, manually operable control buttons for the signal locations constituting the entrance and exit ends of said routes, circuit means responsive to the joint operation of the entrance and exit control buttons for a given route for energizing the associated route relay with the particular polarity to clear the signal at the entrance end of that route, said circuit means being rendered effective only when said manually operable contactor is in the other of its two positions, circuit means for allowing only one of said route relays to be energized at any one time, and a signal control circuit for each signal rendered effective to clear such signal when the route relay for the route over which it governs traffic is energized 10 

